Referring to FIG. 1, a traditional overcurrent protection device 1 is illustrated and comprises a housing 10, a button 11, a first wire terminal 12 and a second wire terminal 13, wherein the button 11 is disposed in a hole 100 of the housing 10. An upper surface of the button 11 is exposed out of the housing 10, while a lower side surface of the button 11 is extended to form a blocking plate 110 which is made of heatproof insulated bakelite material. A spring 15 is sandwiched between a lower end of the button 11 and an inner lower edge of the hole 100. Each of the first wire terminal 12 and the second wire terminal 13 is mounted in the housing 10, respectively. One end of each of the first wire terminal 12 and the second wire terminal 13 is protruded out of the housing 10. Furthermore, the overcurrent protection device 1 further comprises a memory alloy plate 14, wherein one end of the memory alloy plate 14 is connected to the other end of the first wire terminal 12. The other end of the memory alloy plate 14 is provided with a first contact 16 close to an end edge thereof, while the other end of the second wire terminal 13 is provided with a second contact 17 corresponding to the first contact 16. Before the temperature of the memory alloy plate 14 is up to a predetermined temperature, the memory alloy plate 14 is in a bent status, so that the other end of the memory alloy plate 14 is at a position close to the second wire terminal 13.
Therefore, when the overcurrent protection device 1 is in a close mode, the button 11 is forced by the elastic force of the spring 15, so that the blocking plate 110 is sandwiched between the first contact 16 and the second contact 17 to exactly block the electrical conduction therebetween. Then, when the upper surface of the button 11 is pressed to move downward the blocking plate 110, the bent status of the memory alloy plate 14 causes the contact between the first contact 16 and the second contact 17, so that the electrical conduction therebetween is finished. At this time, the overcurrent protection device 1 is switched into an open mode, and the blocking plate 110 is engaged below the first contact 16 and the second contact 17 due to the tight contact between the first contact 16 and the second contact 17. Thus, the button 11 can not move upward based on the elastic force of the spring 15. However, when the current is suddenly raised over a predetermined loading value, and makes the temperature of the memory alloy plate 14 go beyond the predetermined temperature, the other end of the memory alloy plate 14 will deform to reversely bend from the original bent status toward the second wire terminal 13 due to the thermal memory effect, so that the first contact 16 and the second contact 17 will be separated from each other to form a close circuit for switching off the electric power. At this time, because the blocking plate 110 is not engaged below the first contact 16 and the second contact 17, the button 11 can smoothly move upward based on the elastic force of the spring 15. Thus, the blocking plate 110 can return to be sandwiched between the first contact 16 and the second contact 17, so as to prevent the overcurrent protection device 1, wires and related appliances connected thereto from repeatedly receiving the overcurrent over the predetermined loading value due to the recovered bent status of the memory alloy plate 14 after the temperature is lowered. Therefore, the overcurrent protection device 1, wires and related appliances connected thereto can be efficiently protected from possible damage or sparking danger, so that the operational safety of the overcurrent protection device 1 and the appliances can be efficiently enhanced.
However, referring still to FIG. 1, there are still several disadvantages existing in the actual operation of the overcurrent protection device 1, as follows:
(1) When the current is suddenly raised to increase the temperature of the memory alloy plate 14 and deform the memory alloy plate 14 to separate the first contact 16 and the second contact 17, the blocking plate 110 must return to be sandwiched between the first contact 16 and the second contact 17, in order to efficiently prevent the overcurrent protection device 1, wires and related appliances connected thereto from repeatedly receiving the overcurrent over the predetermined loading value. However, because the separation distance of the first contact 16 and the second contact 17 is deformed according to the influence of the temperature of the memory alloy plate 14, the thickness design of the blocking plate 110 for separating the first contact 16 from the second contact 17 is important. If the blocking plate 110 is excessively thick, the blocking plate 110 may not smoothly return to be sandwiched between the first contact 16 and the second contact 17 due to excessively small separation distance of the first contact 16 and the second contact 17 when the current is suddenly raised to heat and deform the memory alloy plate 14 to separate the first contact 16 and the second contact 17, resulting in causing the overcurrent protection device 1, wires and related appliances connected thereto to repeatedly receive the overcurrent over the predetermined loading value. In addition, if the blocking plate 110 is excessively thin, the blocking plate 110 may be easily broken, resulting in losing the protection function of the overcurrent protection device 1. As a result, the overcurrent protection device 1 can not smoothly finish the protection measure of power interruption when the current is overloaded.
(2) When the current is suddenly raised, there are still some risks which may cause that the first contact 16 and the second contact 17 can not smoothly separate from each other. For example, when foreign objects are carelessly placed on the button 11 or when the gap between the button 11 and the housing 10 is filled with dirt over years, the button 11 may difficultly be moved. As a result, the button 11 can not be smoothly moved upward based on the elastic force of the spring 15 for returning the blocking plate 110 to be sandwiched between the first contact 16 and the second contact 17. Therefore, when the current is overloaded under a contact status of the first contact 16 and the second contact 17, the temperature of the memory alloy plate 14 will be raised, and the memory alloy plate 14 will deform to separate the first contact 16 from the second contact 17. Then, after the temperature of the memory alloy plate 14 is lowered under the separation status of the first contact 16 and the second contact 17, the first contact 16 and the second contact 17 will return to contact each other. As a result, not only do the overcurrent protection device 1, wires and related appliances connected thereto repeatedly receive the overcurrent over the predetermined loading value, but also some electric arc may occur between the first contact 16 and the second contact 17 due to the inexact insulation therebetween, resulting in damaging the overcurrent protection device 1, wires and related appliances connected thereto or causing fire accident due to arc sparking.
As a result, it is important for related manufacturers of designing and manufacturing overcurrent protection devices having a trip free mechanism to think how to develop a new overcurrent protection device having a trip free mechanism to solve the foregoing serious disadvantages of the traditional overcurrent protection device.
It is therefore tried by the inventor to develop an overcurrent protection device having a trip free mechanism to efficiently and smoothly separate a first contact from a second contact to automatically switch into an open mode for interrupting the electric power when the current is suddenly raised over the predetermined loading value.